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From our local Electronics Forum came from one member a fantastic idea. This guy has often fantastic ideas that often fall flat on the ground because they do not really coincide with reality.Hating to start a thread/discussion that don't involve my own projects (I never really get the whatever to finish the 5998A-PSE that just recently got a chassis drilled och prepared for this magical amplifier.) I still would like to give you tubaholics a chance to have a view and an opinion.

Let's say you have a smallish bookshelf speaker. It doesn't really go below 100Hz and besides you have only the 12W EL84 PP-amp. Lets say you "boost" both output power and increase attentuation of low freq signals (below 100Hz) and bridge the tube amp with a Class D amp.

Very short about the discussion before I show the plan.I and some other argued that the Class D amp is already bridged and it had two outputs and none was grounded. Another protest as that the intended D-amp was rated 60W and how would the output tranny in the tube amp cope with that and how would the tube amp react to to a signal that was backward injected into the tube amp?

So here's the master plan:

Attachment:

KDP_actual.PNG

The text is in Swedish but shortly this is the intention. The signal is fed to the tube amp and to a 12dB bass boost filter hooked up to the D-amp after the signal has been inverted. If using a D-amp it can, according the plan be hooked up like in the diagram at the bottom - only one output used and capacitive coupled to the speaker.

What reasonable argument (preferable objective and indesputable facts) can be presented against such a hybride? (apart from "it will never work" ).

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_________________Magnus

“If you don't know where you are going, any road will get you there.”―Lewis Carroll

If the solid stage is and tube cut of is matched well at about 100hz then the design could work I belive. The solid stage would be 0v output at higher freq and tube amp takes over acting like bridge but with one side grounded since 0v = ground.Similar when 100hz or below

Hummm.... I would be concerned about phase shifts and phase matching. If any portion of the audio is shifted differently in one amp vs the other it would probably case some nulling and likely to act like a form of IM distortion. There could be some DC level issues as well.

Tube amps show go below 100hz when tuned properly, if it dosen't then most likley its the couppling capcitors betwwen stages or on input made too small.If your so intresting in getting more base then you mayaswell do it the right way

Even if you do manage to get the bridge going your not going to have enough power to get you the midrange volume to go allong with increased base.Your going to get booming base while you have a small volume in vocals which is not what you want.

Best way to get louder volume IMO is to get larger higher senstivity speakers at 101dB like 12-15inch speakers properly crossed over.

If your getting more volume by raw power the return in volume becomes dimishing, further more most amps are probally not going to sound good at high output powers.Most smaller speakers are not good enough at arround 89-92dB and even with 30w rms not going to get me the loud volume I like.

my 15 inch vs a 8 inch makes the diffrence between booming furniture shaking crazy loud vs only kind of loud with same 30w rms due to higher senstivity

I'm guessing the bookself speakers are not rated for 60w rms and its 4inch mostl likeley rated 20-30w rms, going from 15 to 30w rms is 6dB increase in sound volume very small, negltible gains from such expensive setup.

If you use didigal cross over u could get phasefhitless filtering and the system will bridge perfectly.

Another possible solution is to use a all pass filter on both amps to filter out the phase shift effects to match each other

There was a project in good old Popular Electronics for a bass boost filter. I did increase low frequency signals where the speaker started to roll off, giving extra boost , but also made the speaker to roll off faster. I will try that solution myself later and see how good it works.

This project is so ... crazy and I didn't how to deal with it; close my eyes and get involved in better things. But before that I wanted a second opinion.

Taking about opinion, the guy with the bridged D-amp/tube amp is building an ordinary Williamson amp using 807. The rectifier is a heavier 5V3 that is followed by a filter made up by to 33uFcaps. When informed that the datasheet for that tube says 40uF tops, the answer from our friend is that "all components is underrated ....". There's saying that the last idiot isn't born yet ....

_________________Magnus

“If you don't know where you are going, any road will get you there.”―Lewis Carroll

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